East River

1937 - Teen boys making daring dives into the East River.
"Swim in the East River? Without a wet suit, no adult would do it today, let alone allow their child to take a dip there. Yet even after the river became the dumping ground of the city’s untreated sewage, lots of people cooled off in its bracing, choppy waters. Perhaps no group of New Yorkers relied on the river during the hot summer months more than poor tenement kids, who often faced overcrowded public swimming and bathing facilities or preferred the freedom of diving off a city pier with their pals. ..."
Ephemeral New York
W - East River
Into the murky waters: hundreds brave New York City's East River for annual swim (Video)
LA Times: Swim in New York's East River? A floating pool plan envisions a safe way
New Yorker: Swim, Swam, Swum
YouTube: Swimming across the East River